Methods: 40 resin composite discs (12mmx2mm) were made from two light curing RC: a nanohybrid (Enamel Plus HRi, Rosbach, Germany) and a microhybrid (Enamel Plus HFO, Rosbach, Germany). Half of each RC group (n=10) were aged, through 5000 cycles of thermocycling (each cycle consisting in a 30 seconds bath in 5ºC water and a 30 seconds bath in 55ºC water). After aging, all the specimens were placed in coffee, at 37ºC, for 72h, in an incubator. The color was evaluated with a colorimeter and the data was subjected to a qualitative and interpretative analysis.
Results: Resin aging caused a significant decrease of L* value and a non-significant decrease of a* value and increase of b* value. The color change DE* of aging specimens (13,46) was higher than the color change DE* of non-aging specimens (13,22), but not significant (p = 0,675). Enamel Plus HRi resin samples had a higher color change [(18,32) aged and (15,52) non-aged] than Enamel Plus HFO resin [(8,60) aged and (10,93) non-aged]. (p=0,002 for non-aged, p=0,000 for aged).
Conclusion: There were color changes on all the specimens, with aging and with staining. The resin Enamel Plus HRi had the highest color change, so the resin Enamel Plus HFO was considered to have more color stability. The biggest variation was found on L* value, which decreased, displaying less brightness.